Propagation of Electric Dipole Radiation through a Medium

Xin Li,Henk F Arnoldus

doi:10.5402/2012/856748

Abstract

When electromagnetic energy propagates through a material medium, the paths of energy flow may be altered, as compared to propagation in free space. We consider radiation emitted by an electric dipole, embedded in a medium with permittivity and permeability . For a linear dipole in free space, the field lines of energy flow are straight, but when the imaginary part of is finite, the field lines in the material become curves in the near field of the dipole. Therefore, the energy flow is redistributed due to the damping in the material. For a circular dipole in free space, the field lines of energy flow wind around the axis perpendicular to the plane of rotation of the dipole moment. When has an imaginary part, this flow pattern is altered drastically. Furthermore, when the real part of is negative, the direction of rotation of the flow lines reverses. In that case, the energy in the field rotates opposite to the direction of rotation of the dipole moment. It is indicated that in metamaterials with a negative index of refraction this may lead to an observable effect in the far field.

Highlights

When optical radiation from a localized source is observed at a large distance, it appears as if the light travels along straight lines
We shall show that radiation emitted by an electric dipole may have such a vortex structure [4], and such vortices appear in multipole radiation of any order [5]
We have considered the field lines of energy flow for an electric dipole, and we have compared the flow patterns in free space to the flow patterns in an embedding medium

Summary

Introduction

When optical radiation from a localized source is observed at a large distance, it appears as if the light travels along straight lines. Light scattered or reflected by an object seems to travel from the object to an observer along straight lines, known as optical rays These lines are the flow lines of the energy in the radiation field. The first prediction of the existence of an optical vortex was made by Braunbek and Laukien in 1952 [1] They considered the diffraction of a plane wave around the edge of a conducting half plane, and they found that a vortex should appear at the illuminated side of the plane, and close to the edge. Another mechanism that may lead to singularities and vortices in the energy flow is interference. It will be shown that in media the field lines curve due to the presence of the media, and that vortices which are present due to a rotation in the source are altered dramatically by the embedding medium

Electric Dipole Radiation in Free Space

Electric Dipole Radiation in a Medium

Linear Dipole in a Medium

Rotating Dipole in a Medium

Dipole in a Negative Index of Refraction Material

Conclusions